Suspended ceiling systems are widely used in a variety of applications, such as in commercial and residential buildings. Grid-type suspension ceilings cover the plenum area, while still allowing access to the plenum area, which typically contains components of the building's wiring, heating, venting, air conditioning, and plumbing systems, among other mechanical components. A grid of spaced runners and cross-runners are frequently used to position and support the panels. Ceiling tiles or panels are commonly supported in the grid by laying the perimeter of such panels on the panel-support flanges of the runners. The runners and cross-runners are generally suspended from the ceiling using wires, rods, or other suspension runners, among other means, and are arranged and sized according to the shape and size of the panels being supported therein.
The runners are typically made of strips of sheet metal of a minimum thickness folded in a particular cross-section or profile in order to provide an acceptable level of flexural load bearing capacity with relatively little visible downward deflection to safely support the ceiling panels during regular use and during fires as well as to provide an aesthetically pleasing appearance. The sheet metal runners also have a desirable torsional stiffness so that the runners can be easily manipulated when the runners are being hung from a ceiling and attached to other runners during assembly of the ceiling grid. However, the relatively thick sheet metal used to form the runners as well as the relatively large cross-section or profile of the runners increases both the costs of shipping and manufacturing such runners.
One way to strengthen the runner so that a thinner sheet metal can be used and/or so that the cross-section of the runner can be reduced is to interconnect overlapping layers of the runner to form a shear rigid bond between the layers, thereby more effectively absorbing and spreading forces over the overlapping parts of the runner. For instance, inverted T-shaped runners (“grid tees”) have a vertical stalk connected at its base to a horizontal flange and are manufactured by bending a piece of sheet metal so that two opposing plates or webs form the stalk. A bottom plate or capping forms the bottom of the grid tee to cover the crack formed between the two webs forming the stalk. The flange is formed by bending the bottom of each web to extend outward to form two tables on which the capping is placed. When the two webs forming the stalk are connected to each other by an additional fastener, the fastener absorbs torsional forces and spreads the forces more evenly over both webs, thereby reducing the twisting of the webs. Similarly, interconnecting the tables with the capping absorbs and distributes forces resulting in increased flexural load carrying capacity.
One way to interconnect the overlapping webs or layers of the runner is to use adhesive. Using adhesive, however, can cause extra wear and damage to forming tools such as roll formers, presses, or punches that are used to form the runner but that come into contact with the adhesive. This occurs when the roll formers cut and fold the sheet metal into the general shape of the runner and/or the presses form penetrations used to attach further metal parts (clips or splices for example) to the runner or to create openings for cross-tee grid runners or wire hangers required for the installation of the finished grid products. Adhesive that collects on the forming tools may cause the tools to make imprecise cuts, require greater force to make the cuts, cause the tools to malfunction or jam, or may cause an undesirable thermo or chemical reaction with the tools or other parts or machines near the tools resulting in accelerated wear.
It is an object of certain embodiments of the invention to mitigate one or more of these disadvantages.
Another problem is that the adhesive may flow and collect in the folds of the runner. In this case, the pooled adhesive may not compress sufficiently for proper folding of the runner so that its overlapping webs can abut each other. This results in a runner with poor structural characteristics.
To prevent these problems, a high viscosity adhesive may be used that generally cannot flow to parts of the runner that will come into contact with the forming tools. In certain situations, however, a high viscosity adhesive may not be practical. For instance, it may be otherwise more efficient or economical to use low viscosity hot melt or moisture cured adhesives, or application methods such as spraying or certain bead application processes may require a low viscosity adhesive. Furthermore, even with high viscosity adhesives, some manufacturing line speeds move the runners and/or adhesive application equipment so fast that even high viscosity adhesive will be splashed to parts of the runner that receive a forming tool. Finally, some adhesives harden and expand as they set. In these cases, the expandable and hardening adhesives placed between overlapping webs on the runner may undesirably bend or deform the webs as it expands.
According to a first aspect of the invention, there is provided an element for use in a suspended ceiling grid, comprising:                a stalk portion;        a flange portion;        the stalk and flange portion being connected;        and in at least one of the stalk and flange portion, an indent portion adapted to provide an increase in torsional resistance of the element.        
The flange portion may extend laterally on one side of the plane of the stalk portion whereby to provide an element of substantially L-shape in end elevation.
Alternatively, the flange portion may extend laterally on both sides of the plane of the stalk portion, whereby to provide an element of substantially T-shape in end elevation.
There may be at least one distinct indent portion.
Suitably, the stalk portion may comprise at least two substantially parallel opposed web portions.
The flange portion may comprise an upper in use portion with an upwardly facing surface, a capping portion generally disposed beneath in use the upper portion, and at least one overturned portion adapted to connect the upper in use portion and the capping portion.
In a preferred embodiment the overturned portion may extend from below the upper portion to above the upwardly facing surface of the upper in use portion.
There may be an adhesive disposed in one or more of the at least one indent portions.
Suitably, the two opposed web portions may each comprise at least one indent portion.
For ease of manufacture and/or use, the indent portions in opposed web portions may be opposed.
The at least one indent portion may define at least one channel extending longitudinally of the element.
There may be at least two channels which may be substantially parallel with one another and there may be adhesive disposed in more than one of the at least two channels.
There may be adhesive disposed between the upwardly facing surface and the overturned portion.
Suitably, the adhesive may comprise a low viscosity adhesive.
The element may comprise a runner for a suspended ceiling grid, or alternatively may comprise a wall angle for a suspended ceiling grid.
According to a second aspect, the invention provides a runner for a suspended ceiling grid, comprising:                two opposing web portions;        two flange portions;        at least one distinct indent portion;        the at least one indent portion located on                    at least one of the web portions; or            at least one of the flange portions; or            at least one of the web portions and at least one of the flange portions.                        
According to a third aspect, the invention provides a runner for a suspended ceiling grid, comprising:                an upper portion with an upwardly facing surface;        a lower capping portion generally disposed beneath the upper portion;        at least one overturned portion to connect the lower capping portion to the upper portion, the at least one overturned portion extending from below the upper portion to above the upwardly facing surface of the upper portion; and        an adhesive disposed between the upwardly facing surface and the at least one overturned portion.        
According to a fourth aspect, the invention provides a runner for a suspended ceiling grid, comprising;                an upper portion with at least one overturned end portion; and        a lower capping portion with at least one overturned end portion configured and disposed so that the at least one overturned end portion of the lower capping portion extends around the at least one overturned end portion of the upper portion.        
According to a fifth aspect, the invention provides a method of forming an element for a suspended ceiling grid, comprising the steps of:                forming at least one indent on a web member;        placing an adhesive in one or more of the at least one indent; and        after placing the adhesive in one or more of the at least one indent, moving a forming tool on the web member, wherein the at least one indent that contains the adhesive provides sufficient space to substantially maintain the adhesive out of contact with the forming tool.        
According to a sixth aspect, the invention provides a method of forming an element for a suspended ceiling grid, comprising the steps of:                forming at least one indent on a web member;        placing an expandable adhesive in one or more of the at least one indent; and        folding the web member to form two opposing web portions wherein the adhesive is disposed between the two opposing web portions, and wherein the at least one indent has sufficient dimensions to permit the adhesive to expand without substantially deforming the web member.        
According to a seventh aspect, the invention provides a wall angle for a suspended ceiling grid comprising:                a web portion;        a flange portion;        at least one indent portion;        the at least one indent portion located on the web portion, on the flange portion, or on both the web portion and the flange portion.        